Electric discharge tube



Dec; 9, 1958 J. L. H. JONKER ET AL 2,864,026

ELECTRIC DISCHARGE TUBE Filed March 22. 1954 INVENTORS JOHAN' LODEWIJK HENDRIK JONKER HENDRIK GROENDIJK BY @WVg AGENT United States Patent ELECTRIC DISCHARGE TUBE Johan Lodewijk Hendrik Jonker and Hendrik Groendijk,

Eindhoven, Netherlands, assignors, by mesne assignments, to North American Philips Company, Inc., New York, N. Y., a corporation of Delaware Application March 22, 1954, Serial No. 417,776

Claims priority, application Netherlands March 20, 1953 2 Claims. (Cl. 313-293) This invention relates to electric discharge tubes and especially to a tube for amplifying electrical oscillations and suitable for operation with low electrode voltages, more particularly in a device for high-frequency amplification such as, for example, car radio sets. The term low voltages is here to be understood to mean voltages at which no secondary electrons are dislodged by primary electrons.

It is known that electric discharge tubes are adapted to operate with electrode voltages of only a few volts. In order to improve the operation at such very low voltages it has been proposed to provide an accelerating or space-charge grid adjacent to the cathode in order to drain the space charge from the cathode to the effect of increasing the anode current. This, however, has a limitation in that the accelerating grid takes a comparatively heavy current.

The operation of an electric discharge tube suitable for operation with low electrode voltages can be greatly improved if according to the invention, at least one control electrode of the tube is coated with a material having a high work-function whereas the anode is coated with a material having a low Work-function. This combination yields the advantage that the contact potential of the material, with which the control electrode is coated, is negative relative to that of the material of this electrode, so that the surface of this layer attains a more negative potential relative to the cathode surface, which permits the control electrode to be externally connected to the cathode supply conductor without the intermediary of a voltage source and without the grid tending to take current. Since, on the other hand, the anode is coated or treated with a material having a low work-function there will occur a positive potential leap which increases the anode voltage relative to the cathode surface. With such low anode voltages as referred to above, more particularly about 6 volts, an increase by approximately 0.5 volt is quite noticeable.

It has been found that the use of the invention yields a considerable increase in mutual conductance, which is of special importance for high-frequency amplifying tubes, so that they can be completely supplied from a 6 volts automobile accumulator without requiring converters for producing high anode voltages.

Materials appropriate for coating the control electrodes are, for example, gold or platinum, whereas the anode may be coated or treated with barium, caesium or similar alkalior alkaline earth metals.

Preferably a tetrode is employed, since in this case, owing to the low screen-grid and anode-voltage and the resulting low electron velocities, no trouble is experienced from secondary emission by the screen grid or the anode. Hence, similarly to a pentode, the screen-grid voltage may exceed the anode voltage without causing distortion. At such low voltages the tetrode is consequently equivalent to a pentode.

2,864,026 Patented Dec. 9, 1958 Tubes comprising gilded grids and tubes comprising platinum-covered electrodes areknown per se. Furthermore tubes are known, in which .the anode side gfacing the cathode is coated with an alkalior alkaline earth metal, for example caesium. However, these steps are always taken in connection with secondary emission which, however, is not instrumental in the present invention. The combination according to the invention, necessary to obtain the aforesaid effect, has not come to be known previously.

In order that the invention may be readily carried into effect, it will now be described in greater detail with reference to the accompanying drawing, given by way of example, in which Figs. 1 and 2 show graphs of a tube according to the invention.

Fig. 3 shows schematically a circuit employing an electron discharge tube according to the invention.

With reference to Fig. 1, the reference numeral 1 designates the Ia--Vg curve and 2 denotes the Ig -Vg curve of a normal tube. The reference numerals 4 and 3 designate the IaVg and Ig Vg curves respectively of a tube known per se, of which only the control electrode g is coated with gold or platinum. Owing to the contact potential between the goldor platinum layer and the material of the electrode itself, the line 2 shifts towards 3 and the line 1 towards 4. Consequently, the mutual conductance remains unchanged, that is to say the mutual conductance at 5 corresponds to that at 6.

By reducing, according to the invention, the emission potential of the anode, the curve 4 shifts again to the left approximately to its initial position 1 or even therebeyond, if the contact potential leap of the Cs relative to the material of the anode exceeds that of gold or platinum relative to thematerial of the control electrode. It will be evident that the mutual conductance at 7 exceeds that at 5 or 6.

Fig. 2 shows that a pentode curve is obtained since the voltages remain far below the voltage at which secondary emission tends to play a role in a tetrode (line 8). The line 9 is the characteristic curve of a usual pentode. When using the invention the suppressor grid of the pentode can consequently be omitted which constitutes a simplification from a constructional point of view.

Fig. 3 shows a circuit employing one or more tubes according to the invention. Since the tube is designed to operate in circuits in which the plate voltage is in the range of 6 to 12 volts, the plate 10, which is coated with caesium is connected through a load impedance 11 to a battery source 12 having a potential of about 6 volts. Capacitor 13 couples the amplifier stage shown to succeeding stages each of which operate at similar plate voltages.

Grid 14 is connected to ground through impedance 15 and cathode 16 as one terminal connected to battery 12 and the other terminal grounded.

What is claimed is:

1. An electron tube circuit in which the plate voltage supplied to the electron tubes thereof is in the range of 6 to 12 volts, said electron tubes comprising a cathode, a control electrode having a conductive core and coating thereover of a high-work function material for obtaining a negative contact potential for said electrode and thereby rendering said electrode more negative with respect to said cathode, and an anode having a surface coating of a low-work function material for obtaining a positive contact potential thereby making said electrode more positive with respect to said cathode.

2. An electron discharge tube as claimed in claim 1 UNITED STATES PATENTS 1,543,033 Snelling June 23, 1925 Thomas Mar. 5, 1929 Van Overbeek Feb. 7, 1939 Hansell Dec. 31, 1940 Taylor May 5, 1942 

